Author: Calvey, J.R.
Paper Title Page
TUA2WB03
 Modeling Ion Effects for the APS-U  
 
  • J.R. Calvey, M. Borland
    ANL, Argonne, Illinois, USA
  
  Ions are produced in an accelerator when the beam ionizes residual gas inside the vacuum chamber. If the beam is negatively charged, ions can become trapped in the beam's potential, and their density will increase over time. Trapped ions can cause a variety of undesirable effects, including instability and emittance growth. Typically, simulation of ion effects is done using a "weak-strong" model, in which the ions are modeled using macroparticles, but the beam is assumed to be a fixed Gaussian distribution, with only centroid motion allowed. This type of model necessarily neglects incoherent beam effects, such as decoherence, emittance growth, and tune spread. Recently, an IONEFFECTS element has been incorporated into the particle tracking code ELEGANT. The code has been parallelized, and allows for modeling intra-bunch effects, in combination with other elements. Ion effects have been modeled for the APS-U storage ring and Particle Accumulator Ring, using both a weak-strong code and ELEGANT. Some of the questions investigated include ion instability in the presence of train gaps, ion-induced emittance growth, and multiple ionization.  
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